error messages since installing avast non tecky needs help

Installed Avast performed a scan which when finished recommended re-starting with boot-time scan which did and now cannot open iTunes get these two messages MSVCR80.dll missing and error 7 (windows error 126) suggests re-installing which have tried but it same thing happens. Also tried to open Media Go and that shut windows down altogether due to a problem. Also cant open Google earth keeps saying there is a problem. I had none of these problems before doing the scan and boot scan also tried a system restore which didnt solve the errors. Am really worried that the boot scan has erased something important. I am no expert and so fed up with these problems so any help keep simple please wish I had never purchased Avast!!

Installed Avast performed a scan which when finished recommended re-starting with boot-time scan
If avast recomended a boot scan it must have found something in the first scan you did....what file, and what malware name did avast give it?

You may take a screenshot of avast chest (quarantine) and attach

MSVCR80.dll could’ve been corrupt due to a virus or other malware and rightfully removed. Yes, it lead to a problem and that might’ve made you wish you’d never bought Avast, but in fact Avast probably removed a virus you had all along.

Here’s an elaborate how-to on how to repair the problem when iTunes no longer works. Be sure to pay attention to the “note:” and "important:" bits.